The present invention relates to an image scaling method and apparatus converting an input image into a desired image with suitable resolution for application, in the case that the input image and the desired image for application are different in resolution, and more particularly to an image scaling method and apparatus using domain filtering and interpolation method.
As various kinds of digital display apparatuses are popularized, several types of image formats have been utilized.
Generally, images of which resolutions are different from each other are applied to these image formats and therefore the need to convert resolution of an input image arises to adapt to an image display apparatus.
Particularly, real-time conversion of images should be performed in the display of moving images, therefore, the development of the image scaling hardware being of high quality and low cost has been rising in order to achieve those aims.
And particularly, because the resolution of digital display such as TFT-LCD (Thin Film Transistor-Liquid Crystal Display) is fixed according to products, it is requisite to convert various resolutions of input images into the resolution of display itself.
There are many related conventional technologies such as U.S. patent documents including U.S. Pat. Nos. 5,889,895, 5,671,298, 5,500,744, etc.
However, conventional image scaling hardware had several disadvantages in order to be used commonly or commercially, which include low quality of image caused by only repeating pixels and then displaying them, or high cost caused by excessive load of operation and the need of complicated hardware structure.
The present invention relates to an image scaling method and apparatus converting an input image into a desired image with suitable resolution for application, in the case that the input image and the desired image are different in resolution.
A method for image scaling to convert an input image into a desired image with suitable resolution for application is provided. The method comprises:
(a) computing a position of a filter window by setting up the filter window after placing a lattice of pixels with suitable resolution for application on an original image;
(b) determining an area occupancy ratio of the filter window on pixies of the original image from the computed position of the filter widow; and
(c) obtaining a finally filtered image by using the determined area occupancy ratio as a filter coefficient.
Preferibly, the image scaling is performed using domain filtering and/or interpolation method.
Preferably, the position of the filter window is center coordinates and boundary coordinates of the filter window.
More preferably, step (a) further comprises, in the case of magnifying the image:
adding as much as a width of the filter window to x-coordinate values of previous or initial filter window, while moving horizontally; and
adding as much as a width of the filter window to y-coordinate values of previous or initial filter window, while moving vertically.
Preferably, step (b) further comprises:
comparing integer values of center coordinates of the filter window with integer values of four vertexes coordinates and then examining whether the center of the filter window extends adjacent pixels in all directions including the right, left, up, and down sides;
computing an overlapped distance value of the filter window on adjacent pixels, in the case that the center of the filter window extends adjacent pixels in all directions including the right, left, up, and down sides;
determininig a partial area value of the filter window extending adjacent pixels using the overlapped distance value; and
obtaining the area occupancy ratio through multiplication of a scale factor and the partial area value, and wherein the scale factor is expressed as       Scale    ⁢          xe2x80x83        ⁢          Fa      ⁢      ctor        =            1.0              (                  width          ⁢                      xe2x80x83                    ⁢          of          ⁢                      xe2x80x83                    ⁢          filter          ⁢                      xe2x80x83                    ⁢          window          xc3x97          height          ⁢                      xe2x80x83                    ⁢          of          ⁢                      xe2x80x83                    ⁢          filter          ⁢                      xe2x80x83                    ⁢          window                )              .  
More preferably, step (c) further comprises:
sorting the area occupancy ratio in the order of magnitude; and
improving an image quality by altering a weight value through the method of subtracting some constant value from the coefficient value with smaller area ratio and then adding the subtracted constant value to the coefficient value with larger area ratio.
An image scaling apparatus converting an input image into a desired image with suitable resolution for application is provided. The apparatus comprising:
filter coefficient generating means which consists of a filter window interpolator for computing a position of a filter window, and a filter coefficient generator for generating a filter coefficient through a multiplication of a scale factor and pixel""s occupancy area value of the filter window, which is determined from the output value of the filter window interpolator; and
an image generating filter for generating a finally scaled image by utilizing the filter coefficient obtained from the filter coefficient generating means.
Preferably, the apparatus further comprises a prescaler for previously reducing the input image by 2n times (n: integer), in the case of reducing the input image to the image smaller than a half (xc2xd) of itself in either vertical or horizontal direction.
A recording apparatus being able to read the program converting an input image into a desired image with suitable resolution for application through the computer in which the program is recorded, the program comprises:
computing a position of a filter window by setting up the filter window after placing lattice of pixels with suitable resolution for application on an original image;
determining an area occupancy ratio of filter window on pixels of the original image data from the computed position of the filter widow; and
obtaining a finally filtered image by using the determined area occupancy ratio as a filter coefficient.